Add the butter and sugars to a large mixing bowl. Use an electric mixer to beat them together on medium speed for about 2-3 minutes. Once creamed, add in the peanut butter and mix again on medium speed until combined.

Then, add the egg and vanilla extract and beat on a low speed until just combined.

Add in the flour, baking soda and salt. Mix again on a low speed.

Shape the cookie dough into a disc and wrap in plastic wrap. Place in the refrigerator for one hour to chill. Place the mini Reese's cups in the refrigerator to also chill.

After the cookie dough has been chilling for one hour, preheat the oven to 350°F and line two baking sheets with parchment paper.

Create 1-inch balls of dough and place them on the baking sheet about two inches apart. Bake each sheet of cookies one at a time on the middle rack for 10-11 minutes, just until the cookies begin to crack. While the cookies bake, unwrap the Reese's cups and then keep in the refrigerator until use.

As soon as the cookies come out of the oven, gently press a Reese's cup into the center of a cookie. Then, move the cookies to a cooling rack.

Once the cookies are cool, pipe on the spider's legs. Create eight legs by drawing four lines from the Reese's cup outward and down the cookie on each side. Dab two spots of icing to glue the eyes to the body of the Reese's cups.